Method and apparatus for waveform shaping of packet data

Abstract: In the transmitter which carries out burst transmission using information data as a packet, if the status is divided into four modes, namely, burst stop mode, burst rising mode, burst continuous mode, and burst falling mode, a waveform shaping equipment designed to read out shaped waveform data for each mode from outputs of either of the two memory tables, the first memory table which holds waveform data for specific data patterns used in common in burst rising mode and burst falling mode and the second memory table which holds waveform data for all data patterns used in the burst continuous mode, or a waveform shaping equipment comprising the third memory table which holds waveform data corresponding to all the data patterns used in the burst rising mode and the fourth memory table which holds waveform data corresponding to all data patterns used in the burst falling mode and generating shaped waveform data by synthesizing the two outputs of the third and the fourth memory tables at the time of burst continuous mode.

Description: The present invention relates to the waveform shaping equipment and waveform-shaping method for generating bandlimited signals, and for preventing band spread at the head and trail at the edge of burst when burst-like data string is transmitted in the data transmission in which data is transmitted in the form of packet. In the radio communication, etc., when a packet comprising transmission data is transmitted, it is necessary to limit the bandwidth (bandlimitation) to prevent adjacent channel interference for effective utilization of frequency. For bandlimitation of signals, it is common to limit the bandwidth with respect to the signal waveform of the baseband. Two systems are available for band-limiting the baseband signal waveform: an analog system using analog filter and a digital system by digital signal processing. One of the digital systems is the method to shape waveform by reading out and concatenating the baseband signal waveform previously band-limited by calculation from the memory table such as ROM and the like (for example, IEEE Transactions on Communications, COM-Volume 25, No. 10, Pages 1243-1244). When the waveform shaping method using this memory table system is used, the ideal filter frequency response can be more accurately realized than the analog system waveform shaping method, and the shaped waveform can be changed only by rewriting the memory contents, achieving high versatility. It is also suited for the VLSI technique and can be comparatively downsized. Such a digital low pass filter for performing band-limitation in a QPSK modulation circuit is described in EP-A-0 494 696. The filter comprises a read only memory (ROM) which stores segments of convoluted base-band waveforms in order to provide for an inter-symbol interference of a plurality of consecutive symbols. The band-limited waveform for a currently processed symbol is obtained by reading a segment from the memory in accordance with a predetermined number of preceding and succeeding symbols. Referring now to the drawings, the conventional waveform shaping equipment using the above-mentioned method is described with special emphasis placed on the readout principle of shaped waveform and hardware configuration of the waveform shaping equipment. FIG. 1 shows input data to the waveform shaping equipment. D(1), D(2), ....., D(k), ..... D(n) show transmission data and X shows the data other than the transmission data,which does not have any information. Each data is successively read into the waveform shaping equipment at every time interval T. FIG. 2a shows the data pattern comprising each input data of FIG. 1. The data pattern is used to specify part of the address for reading out waveform after bandlimitation from the memory table. In this section, to simplify, description is made supposing that there is an intersymbol interference which has 3 symbols time and the data pattern length is 3 symbols. A(1), A(2), and A(3) show a time slot, respectively. Let the time slot A(2) in each data pattern be the present time slot. Then, time slots A(1), A(3) affect the present time slot A(2) by intersymbol interference. Each data pattern (p(1), p(2), p(3), p(4), data, respectively, and the data pattern p(1) comprises the data (D(1), X, X), the data pattern p(2) comprises the data (D(2), D(1), X), the data pattern p(3) comprises the data (D(3), D(2), D(1)), the data pattern p(4) comprises the data (D(4), D(3), D(2)), the data pattern p(n) comprises the data (D(n), D(n-1), D(n-2)), the data pattern p(n+1) comprises the data (X, D(n), D(n-1)), and the data pattern p(n+2) comprises the data (X, X, D(n)). FIG. 3 shows the case when the data pattern corresponding to the present time slot which varies at every time interval T is extracted. FIG. 2b shows baseband waveform after bandlimitation, which is generated when the waveform is read out from the memory table successively at every 1 symbol time T by the data pattern shown in FIG. 3. That is, the waveform w(3) which has 1 symbol time is generated by the data pattern p(3), the waveform w(4) equivalent to 1 symbol time is generated by the data pattern p(4), and the waveform w(n) equivalent to 1 symbol time is generated by the data pattern p(n). Because in the data patterns p(1), p(2), p(n+1), and p(n+2) indefinite data X with no information is contained, it is designed to output the 0-level waveform as the waveform for w(1), w(2), w(n+1), and w(n+2) at the time corresponding to data patterns p(1), p(2), p(n+1), and p(n+2). FIG. 4 shows one example of a block diagram showing the hardware configuration of conventional waveform shaping equipment. In FIG. 4, S3 denotes a shift register, C3 a counter, M3 a memory table, D3 a D/A converter, and L3 a low-pass filter. dt3 denotes a dta string, co3 a counter output, so3 a shift register output, mo3 a memory output, wd3 a continuous waveform after D/A conversion, w13 a shaped waveform after smoothing. In general, let the data string dt3 be the data string of 2^M value (M: natural number), 1 symbol is M bits and the shift register 101 is made up of M bits x 3 stages. Therefore, the output from each stage becomes M bit each, respectively. For simplification, description will be made assuming that the shift register handles M=1, that is,binary data. The shift register S3 accumulates data for latest 3 bits of the data string dt3, and while taking in 1-bit data from the data string dt3 at every 1 symbol time and shifting, it outputs 3-bit data pattern so3 in parallel. The memory table M3 is a ROM which stores waveform data for one symbol time with the effects of intersymbol interference taken into account by prior calculation. That is, it stores waveform data for all the patterns which the total of 3 bits comprising the symbol to be transmitted and symbols before and after can take. Now, let the waveform data for one symbol time comprise 8 samples. The counter C3 is a 3-bit counter, which counts up 8 times in one symbol time and repeats operation with one symbol time as one cycle. The memory table M3 designates a total of 6 bits as an address, which comprises 3-bit data pattern so3, an output of each stage of the shift register S3, and 3-bit output co3 of the counter C3 which represents the location in one symbol time, retrieves the waveform data at each time corresponding to the data pattern to be transmitted, and outputs the memory output mo3. The memory output mo3 is converted to continuous waveform wd3 at the D/A converter D3 and after smoothed at the low-pass filter L3, it becomes shaped waveform w13. Next discussion will be made on the method for generating baseband signals after bandlimitation in the QPSK using this method. FIG. 5a shows data of the in-phase axis and quadrature axis extracted at every time slot from the transmission data string in the QPSK. Expressing this as a transition state for each time slot on the signal space produces FIG. 6. In FIG. 6, each signal point transitions at each time slot and the locus on the time axis of the orthogonal projection cast on the in-phase axis and quadrature axis of the coordinates of transitioning signal point represents the baseband signal waveforms of the in-phase axis and quadrature axis. FIG. 5b shows the baseband , signal waveform of the in-phase axis and the quadrature axis corresponding to the in-phase axis and quadrature axis data shown in FIG. 5a before bandlimitation. When the baseband signal waveform of the in-phase axis and quadrature axis shown in FIG. 5b are band-limited with the intersymbol interference of the data pattern length taken into account, the baseband signal waveform after bandlimitation as shown in FIG. 5c can be obtained. The in-phase axis signal waveform and the quadrature axis signal waveform make the H level of waveform correspond to the data value "0" and the L level of waveform to "1" as shown in FIG. 5b and 5c. In the case of the QPSK, since the baseband signal waveform of the in-phase axis is determined by the in-phase component of the coordinates of each signal point and that of the quadrature axis by the quadrature component, the data patterns of the in-phase axis and the quadrature axis can be obtained separately from the in-phase component and the quadrature component in the time slot. In addition, because the baseband signal waveforms for the same data pattern of the in-phase and quadrature axes become identical, the waveform data necessary for shaping baseband signal waveforms of in-phase and quadrature axes can be used in common. Consequently, the storage capacity can be reduced as shown in, for example, JP-A-01 317090. FIG. 7 is a block diagram of waveform shaping equipment for the QPSK by the above-mentioned conventional method. In FIG. 7, C6 is a clock generation circuit, DV6 a 1/2 frequency divider, DP6 a 2-bit shift register, SR6I a d-bit shift register, SR6Q a d-bit shift register, CO6 a n-bit counter, DS6 a data selector, M6 a L-bit output memory table, SR6 a L-stage 2-bit shift register, FF6I a flip-flop, FF6Qa flip-flop, PI6 a π-phase shift circuit, D6I a D/A converter, D6Q a D/A converter, L6I a low-pass filter, and L6Q a low-pass filter. ck6 is a system clock, ckd6 a divided clock, ckp6 a π-phase shift clock, dt6 a data string, dt6I an in-phase axis input data, dt6Q a quadrature axis input data, so6I an output of shift register SRI6, so6Q an output of shift register SRQ6, co6 a counter output, mo6 a memory output, wd6I an output of D/A converter D6I, wd6Q an output of D/A converter D6Q, w6I shaped continuous waveform of the in-phase axis, and w6Q shaped continuous waveform of the quadrature axis. For simplification, description will be made when the equipment treats the case in which d=3, n=2, and L=3. The shift register DP6 takes the data string dt6 at every 1 clock while shifting, retains the latest 2-bit data, and outputs by allotting one bit each to the shift register SR6I and the shift register SR6Q. The shift register SR6I and the shift register SR6Q take in the output of shift register DP6 one bit at a time as in-phase axis data dt6I and quadrature axis data dt6Q while shifting every 2 clocks by the divided clock ckd6, hold the latest 3-bit data, respectively, and output the shift register output so6I and shift register output so6Q in parallel as a 3-bit data pattern for the in-phase axis and quadrature axis, respectively. Now, the waveform data for 1 symbol time comprises four samples, and using the 2-bit counter CO6 whose 1 symbol time is 1 cycle, part of the address of waveform data to be read out within one symbol time is specified based on the counter output co6. The memory table M6 which has a 3-bit output is a ROM which stores waveform data for 1 symbol time with the effects of intersymbol interference taken into account by prior calculation. That is, the ROM stores waveform data quantized by 3 bits for all patterns which can be taken by the total of 3 bits comprising the symbol to be transmitted and those before and after it. The shift register output so6I and shift register output so6Q which are data patterns of the in-phase axis and quadrature axis time-share the waveform data in the memory table M6 by being selected by the data selector DS6 alternately and becoming part of the address. The 3-bit memory output mo6 read out alternately from the data pattern of the in-phase axis and quadrature axis, respectively, are allotted to the flip-flop FF6I and flip-flop FF6Q by the 2-bit 3-stage shift register SR6, which shifts every 1 clock, and are taken in simultaneously to the flip-flow FF6I and flip-flop FF6Q by the clock timing ckp6 generated by the π-phase shift circuit PI6. In addition, the outputs of the flip-flop FF6I and flip-flop FF6Q are converted to the analog waveform wd6I of the in-phase axis and the analog waveform wd6Q of the quadrature axis via the D/A converter D6I and D/A converter D6Q, and after smoothed at the low-pass filter L6I and the low-pass filter L6Q, they are formed into the shaped waveform w6I, which is the baseband signal of the in-phase axis, and the shaped waveform w6Q, which is the baseband signal of the quadrature axis. FIG. 8 shows operation timing of each section of the equipment. In the case of QPSK, it has been possible to reduce the memory capacity to one half, which is required to store waveform data by the waveform shaping equipment shown in FIG. 7. However, in the case of quadrature modulation in which the in-phase axis and quadrature axis baseband signal waveform to be read out must be determined based on both in-phase and quadrature components of the coordinates of the signal point corresponding to the transmission data, for example, in the π/4 shift QPSK and in the PSK-VP (phase shift keying with varied phase) system described in Pages 412-419 of the proceedings of the 40th IEEE Vehicular Technology Conference), it is impossible to extract the in-phase component and quadrature component data independently at the in-phase axis and quadrature axis for each time slot and form a data pattern. This will now be described by way of example in the case of the π/4 shift QPSK. FIG. 9a shows the transmission data for each time slot in the π/4 shift QPSK. The signal point corresponding to the transmission data of each time slot takes the transition state as shown in FIG. 10 on the signal space. In FIG. 10, A9e shows the quadrature coordinate axis corresponding to the even-number time slot, and A9o shows the quadrature coordinate axis corresponding to the odd-number time slot when the quadrature coordinate axis A9e is rotated 45°. In FIG. 10, the signal point transitions every even-number time slot and odd-number time slot with the quadrature coordinate axis varied, and the locus of the orthogonal projection which the coordinates of the transitioning signal point cast on the in-phase axis and quadrature axis on the time axis represents the baseband signal waveform of the in-phase axis and that of the quadrature axis. FIG. 9b shows the baseband signal waveforms of the in-phase and quadrature axes before bandlimitation, which correspond to the transmission data shown in FIG. 9a. Band-limiting to the in-phase and quadrature axes baseband signal waveforms shown in FIG. 9b, produces the intersymbol interference and can provide the baseband signal waveform after the bandlimitation as shown in FIG. 9c. In the case of π/4 shift QPSK, in-phase and quadrature baseband signal waveforms corresponding to the transmission data depend on both in-phase and quadrature components of the coordinates of the signal point. That is, this is also apparent from the fact that the in-phase baseband signal waveforms read out at the time slots t4 and t6 shown in FIG. 9b differ because in the even-number time slots t4 and t6 of FIG. 9a, each in-phase component takes the same data value "1," but each quadrature component differs. This means that for reading out waveform for both in-phase and quadrature axes, it is necessary to use as part of the address (1) the data pattern which comprises double bit number including both in-phase and quadrature components for each time slot and (2) the signal which selects quadrature coordinate axis either A9e or A9o respectively. In the case of π/4 shift QPSK, the same data pattern is used for the in-phase and quadrature axes, but because the baseband signal after bandlimitation of in-phase axis and quadrature axis to be read out for the same data pattern differs, respectively, it is unable to take a configuration to time-share the memory table as shown in FIG. 6 and it must be designed to store in separate memory tables, respectively, the baseband signal waveforms in all cases with the effects of inter-symbol interference from several symbols for the in-phase and quadrature axes taken into account. However, in the configuration in which all the baseband signal waveforms for the above in-phase and quadrature data patterns are stored in separate memory tables, respectively, suppose that the number of symbols which have effects on the intersymbol interference is d, the number of samples in one symbol is n, and the quantization bit number of waveform data is L, the memory capacity required to retain the waveform data becomes 2 x 2^(3d) x L x n bits in the case of the π/4 QPSK and 2 x 2^(2d) x L x n bits in the case of the QPSK-VP, creating a problem that the memory capacity greatly increases as compared to 2^d x L x n bits of the QPSK. When burst-like data strings are transmitted by each of the above systems, for example, in the case of FIG. 2b, abrupt rise and fall of waveform occur at the burst edge at the head and the trail of the data string at non-continuous points qb and qc, causing the spectrum to spread and the band to expand. Consequently, it becomes also necessary to shape the waveform smoothly at the burst edge. Conventionally, in waveform shaping at this kind of the burst edge, for example, as described in JP-A-04 058 622, waveform shaping is generally carried out by installing a variable gain amplifier or a variable attenuator at the portion where the waveform is amplified and varying the gain or attenuation rate smoothly at the start and at the end of data string. The conventional burst waveform shaping equipment using the above-mentioned method will now be described with reference to the accompanying drawings. FIG. 11 is a block diagram illustrating a conventional burst waveform shaping equipment and FIG. 12 is a diagram showing waveform at each section of the burst waveform shaping equipment in FIG. 11. In FIG. 11, WG10 is a continuous waveform shaping means, VA10 a variable gain amplifier, and CS10 a gain control signal generating means. In FIGs. 11 and 12, dt10 is a data string, wo10 a shaped continuous waveform, vo10 an output signal, and co10 a gain control signal. The data string dt10 is the burst-like data composed by arranging preamble pre, information data info, and postamble post in that order as shown in FIG. 12. Of these, info is the data string to be transmitted and pre and post are data strings which do not carry information. The contents of pre and post may be optional but at this point, as an example, the 0101 4-bit data string is assumed for both. The continuous waveform shaping means WG10 is a circuit similar to the above-mentioned waveform shaping equipment and outputs shaped continuous waveform wo10 which is shaped to have smooth waveform at the data continuing portion. At first, the gain control waveform generating means CS10 generates the gain control signal co10 and controls the gain of the variable gain amplifier VA10. In this event, when the gain control signal co10 is zero, the gain of the variable gain amplifier VA10 is zero and as the gain control signal co10 increases, the gain also increases. The gain control signal co10 is zero in the period without data, smoothly increases from zero to a specified level in the period of preamble, holds the specified level during the period of information data, and smoothly decreases to zero from the specified level in the period of postamble. Consequently, the output signal vo10 outputted by the variable gain amplifier VA10 has a zero amplitude during the period without any data string to be transmitted, smoothly increases the amplitude in the preamble interval before the data string to be transmitted starts, and smoothly decreases the amplitude in the postamble interval when the data string to be transmitted ends. With the above-mentioned operation, the output signal vo10 is obtained by multiplying the output of the continuous waveform shaping means by the gain waveform of the variable gain amplifier, and because the waveform smoothly varies even at the head and the trail of the data string, the spread of spectrum during transmission of the burst-like data can be prevented. When carrier transmission is carried out, it is common to generate baseband waveforms as the shaped continuous waveform wo10 and to carry out burst shaping using a variable gain amplifier at the high-frequency amplified portion after the carrier is modulated with wo10. However, with the above-mentioned configuration, a variable gain amplifier for burst shaping and a gain control means are required in addition to the continuous waveform shaping means. Furthermore, to prevent spectrum spread, it is necessary to hold the gain change adequately gentle; this requires at least several symbols for the preamble and postamble lengths during the period when the gain is varied. An object of this invention is to provide an improved waveform shaping equipment which can achieve waveform shaping during data continuation and can prevent band spread at the head and the trail of burst. This object is achieved by the features of claim 1 for a waveform shaping equipment. Further embodiments are the subject-matter of dependent claims. The present invention generates pulse waveforms for the predetermined data patterns for the predetermined period at the burst edge during packet transmission under the above-mentioned configuration to eliminate noncontinuous points of signal waveforms, thereby achieving waveform shaping free from the spread of band. By dividing in advance the pulse waveforms for one symbol data into two parts: the first half and the second half,and storing the pulse waveforms in the memory table, there is no need to store waveforms of all the cases with intersymbol interference from several symbols taken into account, and when the packet transmission begins, waveform smoothly rises to output the first waveform, which is the first half of the pulse waveform, and when the packet transmission finishes, waveform smoothly falls to output the second waveform, which is the second half of the pulse waveform, and during the period when transmission data continues in the packet, the third waveform which is the sum of the second waveform which is the second half of the pulse waveform for the preceding data and the first waveform which is the first half of the pulse waveform for the succeeding data is continuously outputted, realizing the waveform shaping free from band spread. Because the present invention constitutes the first memory unit and the second memory unit with semiconductor memory, it can employ a configuration method suited for the VLSI technique, and can store either the first half or latter half of pulse waveform only for one symbol data, thereby requiring only a small memory capacity. According to the present invention, because during the period with no data string to be transmitted, the output waveform is made to the zero level, and at the head of the data string to be transmitted, the first waveform which is the first half of the band-limited pulse waveform is outputted, and during the period thereafter to the trail of the data string to be transmitted, the third waveform which is the sum of the above-mentioned first and the second waveforms is outputted, and at the trail of the data string to be transmitted, the second waveform which is the second half of the band-limited pulse waveform is outputted, burst shaping and waveform shaping at the time of data continuation can be achieved with the same equipment, and burst shaping is enabled in a short time without requiring the preamble and postamble. FIG. 1 is a diagram illustrating of transmission data for each unit time T. FIG. 2a is a diagram illustrating of the data pattern. FIG. 2b is a diagram illustrating the baseband signal waveform after bandlimitation, which is read out based on the data pattern. FIG. 3 is a diagram illustrating time sequence of the data pattern when the data pattern length w is set to 3. FIG. 4 is a schematic block diagram illustrating a prior art waveform shaping equipment. FIG. 5a is a diagram illustrating transmission data for each time slot in conventional QPSK waveform shaping equipment. FIG. 5b is a diagram illustrating baseband signal waveform of the in-phase and quadrature axes before bandlimitation based on the transmission data diagram shown in FIG. 5a. FIG. 5c is a diagram illustrating baseband signal waveform of the in-phase and quadrature axes after bandlimitation based on the transmission data diagram shown in FIG. 5a. FIG. 6 is a diagram illustrating the constellation in the QPSK based on the transmission data diagram shown in FIG. 5a. FIG. 7 is a block diagram illustrating one configuration of a conventional QPSK waveform shaping equipment with reduced memory capacity. FIG. 8 is a diagram illustrating operation timing at each section in the equipment of FIG. 7. FIG. 9a is a diagram illustrating the transmission data for each time slot in the conventional π/4 shift QPSK waveform shaping equipment. FIG. 9b is a diagram illustrating baseband signal waveform of the in-phase and quadrature axes before bandlimitation based on the transmission data diagram shown in FIG. 9a. FIG. 9c is a diagram illustrating baseband signal waveform of the in-phase and quadrature axes after bandlimitation based on the transmission data diagram shown in FIG. 9a. FIG. 10 is a diagram illustrating the constellation in the π/4 shift QPSK based on the transmission data diagram shown in FIG. 8. FIG. 11 is a block diagram of a conventional burst waveform shaping equipment. FIG. 12 is a diagram illustrating signal waveforms of each section of the conventional burst waveform shaping equipment. FIG. 13 is a block diagram of waveform shaping equipment of the first embodiment of the present invention. FIG. 14 is a diagram illustrating waveform data which the waveform generating means has in the same embodiment. FIG. 15 is a diagram illustrating signal waveform of each section in the same embodiment of the present invention. FIG. 16 is a block diagram illustrating the waveform shaping equipment of the second embodiment. FIG. 17 is a diagram illustrating signal waveform of each section in the same embodiment of the present invention. FIG. 18 is a block diagram illustrating the waveform shaping equipment of the third embodiment. FIG. 19 is a block diagram illustrating the waveform generator of the fourth embodiment. FIG. 20 is a diagram illustrating signal waveform of each section in the same embodiment of the present invention. FIG. 21 is a block diagram illustrating the waveform shaping equipment of the fifth embodiment of the present invention. FIG. 22 is a diagram illustrating signal waveform of each section in the same embodiment. FIG. 13 is a schematic block diagram illustrating a waveform shaping equipment in the first embodiment of the present invention. In FIG. 13, J111 denotes a pulse waveform generating means, which comprises an address generating means J117 and memory tables J115 and J116. The address generating means J117 comprises a shift register J118 and counter J119. J112 denotes a waveform processing means, which comprises a waveform adding means J113, waveform selecting means J114, and selecting signal generating means J1111. J1110 is a D/A converter. Jlld denotes data strings, J11d1 and J11d2 are the first-stage output and the second-stage output of the shift register J118, respectively, J11c is a counter output, J11w0 is a zero-level waveform, J11w1 is the first waveform, J11w2 is the second waveform, J11w3 is the third waveform, J11w4 is a shaped waveform, Jllb is a burst control signal, J11s is a selecting signal, and J11w5 is an analog signal. Now, each symbol of data string Jlld is a binary symbol of either 0 or 1 and is transmitted bit by bit per one symbol time. The burst control signal Jllb controls the start and the end of the data string to be transmitted of the data string J11d. FIG. 14 illustrates the waveform data which is stored in advance in the memory tables J115 and J116. In the memory table J115, the first waveform data shown in FIG. 14 a and FIG. 14-b and the second waveform data shown in FIG. 14-c and FIG. 14-d are stored. However, the first and the second waveforms are waveforms for the first half and the second half of the pulses for 1 symbol data, respectively. In this event, a positive polarity pulse is used for the data "0" and a negative polarity pulse is used for the data "1." For the pulse for one symbol data, the waveform which converges within two symbol times in all is assumed. Each waveform data comprises 8 sample data per 1 symbol time. Consequently, memory tables J115 and J116 store a total of 16 samples each of data, 8 samples for 1 symbol time for data "0" and 8 samples for 1 symbol time for data "1," respectively. In FIG. 13, the data string Jlld is first inputted to the shift register J118. The shift register J118 shifts the data every 1 symbol time and outputs in parallel the first-stage output J11d1 and the second-stage output J11d2. In the following description, one symbol time from the point in which the shift register J118 shifts the data to the point in which it shifts the data next is called the symbol interval. The counter J119 is a 3-bit counter which counts up every one-eighth symbol time and repeats counting at the intervals of 1 symbol time. The counter output J11c is a 3-bit binary symbol which counts up successively from "000" to "111" in each symbol interval. The addressing signal generating means J117 comprises a shift register J118 and a counter J119, and feeds 4-bit address with the most significant bit as J11d1 and J11d2 and three low-order bits as J11c to memory tables J115 and J116, respectively. With the address generated as above, the memory tables J115 and J116 output the first waveform J11w1 and the second waveform J11w2. The first waveform J11w1 takes the waveform data of FIG. 14-a and FIG. 14-b successively from the left when J11d1 is "0" and "1," respectively, in each symbol interval. The second waveform J11w2 takes the waveform data of FIG. 14-c and FIG. 14-d successively from the left when J11d2 is "0" and "1," respectively, in each symbol interval. The waveform adding means J113 adds the first waveform J11w1 and the second waveform J11w2 and outputs the third waveform J11w3. The waveform selecting means J114 inputs the first waveform J11w1, the second waveform J11w2, the third waveform J11w3 and the zero-level waveform J11w0, selects either one in accordance with the selecting signal J11s, and outputs it as shaped waveform J11w4. In this event, the zero-level waveform J11w0 is a waveform whose value is constantly zero; for example, when two's-complement representation is used, this can be achieved by constantly bringing all bits to zero. FIG. 15 illustrates waveforms of each section of the waveform shaping equipment of FIG. 13. In FIG. 15, signals taking digital values are expressed by converting them into analog values. In FIG. 15, of the data strings Jlld, the portion of information data info is the data to be transmitted, which occurs in the burst form. The burst control signal Jllb is a signal for indicating the start and the end of data to be transmitted and becomes a high level during the period from the start to the end of information data info and in the period other than the above, it becomes low level. The contents of the data string before and after the information data info may be optional, but in this embodiment, operation will be described with the contents all designated to zero for convenience. The data string Jlld is inputted into the shift register J118 and the data for the latest 2 bits is retained. From the memory table J115, the first half of either positive polarity or negative polarity pulses are outputted in accordance with the first-stage output J11d1 of the shift register J118. Because in this event J11d2 varies 1 symbol time delayed from J11d1, the polarity change of the second waveform occurs 1 symbol time delayed with respect to the polarity change of the first waveform as shown in FIG. 25. That is, in each symbol interval, the second waveform represents the latter half of the pulse corresponding to the preceding data and the first waveform the first half of the pulse corresponding to the succeeding data. The third waveform J11w3 which is the sum of the first waveform J11w1 and the second waveform J11w2 represents the waveform generated by interference between the preceding and succeeding data in each symbol interval, and covers the area from the center of the pulse corresponding to the preceding data and the center of the pulse corresponding to the succeeding data. Consequently, the waveform successively arranging the third waveforms generated in each symbol interval is the waveform superimposing pulses corresponding to each symbol of the data string Jlld, and is a waveform shaped output for the continuous data. Next description will be made on the operation at the start and the end of the information data info. The selecting signal generating means J1111 generates the selecting signal J11s and controls operation of the waveform selecting means J114. The selecting signal J11s is, in general, a 2-bit signal and the four kinds of values which the signal can take are now expressed as 0, 1, 2, 3. The waveform selecting means J114 selects the zero level signal J11w0 when the selecting signal J11s is 0, the first waveform J11w1 when it is 1, the second waveform j11w2 when it is 2, and the third waveform J11w3 when it is 3, respectively, and outputs them as J11w4. The selecting signal J11s takes 1 in the symbol interval just after the start of the information data info, 3 from the next symbol interval to the end of information data info, and 2 from the end of information data info to the next symbol interval as shown in FIG. 15. And in the area other than the above, it takes 0. Therefore, the shaped waveform J11w4, which is the selector output, is a zero-level waveform J11w0 up to the start of the information data info, and the waveform smoothly rises from the zero level because from the start of the information data info to 1 symbol time the waveform becomes the first waveform which is the first half of the pulse for the first bit. Thereafter to the end of the information data info, the third waveform occurs and from the end of the information data info to one symbol time, the second waveform which is the latter half of the pulse for the last pulse is generated. This causes the waveform to converge to the zero level with a smooth trailing. Thereafter the waveform becomes the zero-level signal J11w0 again. With the above operation, the shaped waveform J11w4 becomes smoothly shaped waveform throughout the whole period including the start and the end of the data to be transmitted in transmission of burst-like information data. Lastly, the D/A converter J1110 converts the shaped waveform J11w4, which is a digital signal waveform, to an analog waveform and obtains a smoothly shaped burst-like analog output J11w5. In the above first embodiment, the first and the second waveforms are designated to be simple positive-polarity or negative-polarity pulses as shown in FIG. 14, but they are not limited to these but may be more complicated pulse waveforms or modulated waveforms. The data string Jlld is designated to be the binary string of either "0" or "1," but it is not limited to these, but may be multilevel symbols. For example, if the data string Jlld is a string of 2^M level symbol, the shift register J118 is configured in M bit x 2 stages and J11d1 and J11d2 become M-bit signals, respectively. The first and the second waveform are designated to have 8 samples per 1 symbol time but they are not limited to these but may have optional number of samples. In order to express the start and the end of the data string to be transmitted, the burst-like control signal Jllb is designed to be used but other methods may be used; for example, a method to feed data start signals and data end signals separately or a method to multiplex information of the starting time and ending time in the data string itself may be used. In the above first embodiment, if the present invention is applied to continuous data transmission, not to burst transmission, it can be designed to eliminate the waveform selecting means J114 and the selecting signal generating means J1111 and to constantly D/A convert the third waveform J11w3. Next, the second embodiment will be described. FIG. 16 is a schematic block diagram illustrating a waveform shaping equipment in the sixth embodiment of the present invention. In FIG. 16, J141 denotes a waveform adding means which comprises an adder J1430 and latches J1412, J1413. J1414 denotes a cut-off signal generating means. The waveform processing means J142 comprises with these components. Because other portions are the same as those of the first embodiment in FIG. 13, the description on which will be omitted. FIG. 17 illustrates the signal waveform of each portion of the waveform shaping equipment of FIG. 16. In FIG. 17, signals taking digital values are converted to analog values for indication. In FIG. 16, latches J1412 and J1413 uses the first waveform J11w1 and the second waveform J11w2 as input signals, respectively, and outputs signals same as those of input signals or zero-level signals in accordance with the reset signals J14r1 and J14r2. That is, they assume responsibility for cutting off the inputs to the waveform adding means J143, respectively. In this case, J14r1 and J14r2 are assumed to be positive logic reset signals. That is, the output J14w10 of latch J1412 becomes J11w1 when J14r1 enters low level,and enters zero level when it enters high level, and similarly, the output J14w20 of latch J1413 becomes J11w2 when J14r2 enters low level, and zero level when it enters high level. The cut-off signal generating means J1414 generates reset signals J14r1 and J14r2 as shown in FIG. 17 from timing of the change of burst control signal Jllb. This brings the input of the waveform adding means J143 partially to the zero level and controls the output waveform of the adder. First of all, up to the start of information data info, both J14r1 and J14r2 are at the high level. At the start of information data info, J14r1 changes to low level but J14r2 is held to high level and after the next symbol interval, both J14r1 and J14r2 change to high level. Consequently, as shown FIG. 17, J14w10 becomes the first waveform in the interval from the start to the end of the information data info, and in other intervals, changes to zero level. J14w20 becomes the second waveform in the interval from the next symbol interval of the start of the information data info to the next symbol interval of the end of the information data info, and in other intervals, changes to zero level. The adder J1430 adds J14w10 and J14w20 and obtains shaped waveform J14w4 as an output. As clear from FIG. 15 and FIG. 17, this is identical to that of shaped waveform 11w4 in the first embodiment. That is, it becomes the first waveform during 1 symbol time from the start of information data info and smoothly rises, and thereafter to the end of information data info, it becomes the third waveform which is the sum of the first and the second waveforms, and then, smoothly falls as the second waveform for 1 symbol time from the end of information data info. Finally, D/A converter J1110 converts the shaped waveform J14wk, which is a digital signal waveform, to analog waveform and obtains the analog output same as that of the first embodiment. By the way, in the second embodiment described above, latches J1412 and J1413 are used to bring J14w10 and J14w20 to zero level, but any circuits other than latches can be used if they can control passing and cut-off of input of the waveform adding means J143; for example, a circuit which fixes either one of the two input selectors to zero level may be used. Next discussion will be made on the third embodiment. FIG. 18 illustrates a block diagram of the waveform shaping equipment of the third embodiment. The waveform shaping equipment of this embodiment is designed to generate band-limited two baseband signals to be applied for quadrature modulation such as quadrature phase shift keying. In FIG. 18, J1615 is a serial-parallel converter, J168I and J168Q are shift registers, J165I,J166I, J165Q and J166Q are memory tables, J1612I, J1613I, J1612Q and J1613Q are latches, J1614 is a cutoff signal generating means, J1630I and J1630Q are adders, J1610I and J1610Q are D/A converters. In FIG. 18, data string Jlld is converted to 2-bit serial data strings by the serial-parallel converter J1615 and one data string is fed to the shift register J168I and the other to the shift register J168Q. After two shift registers J168I and J168Q, two systems of the circuit basically similar to the wave shaping equipment of FIG. 16 in the sixth embodiment and generate waveforms of baseband signals for in-phase axis (I axis) and those for quadrature axis (Q axis), respectively. What differs from the equipment of FIG. 16 is that both outputs of two systems of shift register J168I and J168Q are fed as address of the memory table. In this embodiment, because one symbol data comprises 2 bits, the relevant waveform generating means have four types of waveform data for one symbol time comprising 8 samples, respectively, and selects either one type by combining 2-bit data for output. The counter J169 and cutoff signal generating means J1614 are same as those shown in FIG. 16 in the second embodiment, and these outputs can be shared in the circuits for I axis and Q axis, thereby allowing only one system to be provided. As described above, the present invention is also suited for application where waveform shaping is carried out for baseband signals for quadrature modulation or multilevel modulation in carrier transmission. Now, the fourth embodiment is described. FIG. 19 is a block diagram illustrating the pulse waveform generating means in the waveform shaping equipment in the fourth embodiment according to the present invention. Portions other than the pulse waveform generating means are same as those of the first embodiment. In FIG. 19, J1716 is a memory table, J1717, J1718 are shift registers for waveform data, J1719 is a timing generator, and J1720 is a multiplexer. The shift register J178 is the same as that shown in FIG. 13 in the first embodiment. The pulse waveform generating means J171 comprises the above components. FIG. 20 illustrates the timing of signals of each section of FIG. 19. The memory table J1716 stores only the data equivalent to FIG. 14-a and FIG. 14-b. What is characteristic in the present embodiment is that as waveform data, the first waveform and the second waveform are designed to be symmetrical with regard to time. With this configuration, even if waveforms equivalent to FIG. 14-a and FIG. 14-b only are stored, using these inverted with regard to time can produce waveforms equivalent to FIG. 14-c and FIG. 14-d. The memory table J1716 has 1-bit address inputs, according to which 8-sample data of FIG. 14-a and FIG. 14-b can be outputted in parallel. Shift registers J1717 and J1718 take in 8-sample waveform data outputted by the memory table J1716 and output 1 sample at a time while shifting. However, these two shift registers shift in the opposite directions. The timing generator J1719 generates load signals J171d1, J171d2 and clock J17ck of the timing shown in FIG. 20 and feeds them to shift registers J1717 and J1718. However,J171d1 and J171d2 are negative logic load signals and shift registers J1717, J1718 load data in series when they are at low level. When J171d1 or J171d2 are at high level, the shift register J1717 or J1718 shifts data at the rising edge of clock J17ck for output. In addition, the timing generator generates multiplexer control signal J17m and feeds to the multiplexer J1720. The multiplexer J1720 selects either of the first-stage output J17d1 or the second-stage output J17d2 of the shift register J178 and outputs as J17d3. J17d3 serves as an address of the memory table J1716. Timing of J17d3 shall conform to that shown in FIG. 20. However, in the periods other than those stated J17d1 and J17d2, the value of J17d3 may be indefinite. The shift registers J1717 and J1718 load waveforms to the rising edge of each symbol interval in accordance with J17d1 and J17d2, and while shifting in the direction opposite to each other, the waveform data is outputted successively. With the above mentioned action, the shift register J1717 outputs waveform of FIG. 14-a or FIG. 14-b as first waveform J17w1 in accordance with J17d1. The shift register J1718 outputs waveform obtained by time-inverting FIG. 14-a or waveform obtained by time-inverting FIG. 14-b as second waveform J17w2 in accordance with J17d2. In addition, the memory table J1716 requires only to possess data equivalent to FIG. 14-a and FIG. 14-b, enabling this embodiment to reduce the memory table capacity to one half that of the fifth embodiment. Now, the fifth embodiment is described. FIG. 21 illustrates the pulse waveform generating means in the waveform shaping equipment in the fifth embodiment according to the present invention. Portions other than the pulse waveform generating means are same as those of the first embodiment. In FIG. 31, J1916 is a memory table, J1921 and J1922 are multiplexers, J1923 is a timing generator, J1924 and J1925 are counter, and J1926 to J1929 are latches. The shift register J198 is the same as that shown in FIG. 13 in the first embodiment. The pulse waveform generating means J191 comprises the above components. FIG. 22 illustrates the timing of signals of each section of FIG. 21. In this embodiment as well, the first waveform and the second waveform are designed to achieve symmetrical relationship with regard to time same as in the fourth embodiment, and the memory table J1916 stores only the data corresponding to FIG. 14-a and FIG. 14-b in the same manner as in the fourth embodiment. What differs from the fourth embodiment is that the memory table J1916 has 4-bit address inputs in the same manner as in the case of first to third embodiments and outputs data one sample at a time. First of all, counters J1924 and J1925 are 3-bit counters and count up and count down in each symbol interval, respectively, and generate counter outputs 19c1 and J19c2 as shown in FIG. 22. Next, the timing generator J1926 generates multiplexer control signals J19m as shown in FIG. 22 and controls multiplexers J1921 and J1922. With these signals, the multiplexer J1921 selects J19d1 and J19d2 alternately and outputs J19d3 shown in FIG. 22. The multiplexer J1922 selects counter outputs J19c1 and J19c2 alternately and outputs J19d1 shown in FIG. 22. Using these as addresses, the memory table J1916 outputs alternately the data of selecting each sample of waveform of FIG. 14-a or FIG. 14-b corresponding to J19d1 successively from the left and the data of selecting each sample of waveform of FIG. 14-a or FIG. 14-b corresponding to J19d2 successively from the right. That is, it outputs the data corresponding to the first waveform J19w1 and the data corresponding to the second waveform J19w2 alternately by time-sharing sample by sample. The timing generator J1923 further generates clock signals J19ck1, J19ck2, and J19ck3 shown in FIG. 22 and feeds J19ck1 to latch J1926, J19ck2 to latch J1927, J19ck3 to latches J1928 and J1929, respectively. The latch 1926 takes in and holds the data corresponding to the first waveform at the rising edge of J19ck1 and the latch 1927 takes in and holds the data corresponding to the second waveform at the rising edge of J19ck2. Finally, because outputs of latches J1926 and 1927 have their change timing not synchronized each other, latches J1928 and J1929 align timing of signals of these two systems at the rising edge of J19ck3 and output the first waveform J19w1 and the second waveform J19w2, respectively. As described above, in this embodiment as well, in the same manner in the fourth embodiment, the memory table capacity can be reduced to one half from that of the first embodiment. In addition to this, because the first waveform data and the second waveform data are read alternately from the memory table sample by sample by time sharing, shift registers J1717, J1718 of the fourth embodiment can be eliminated and the circuit can be simplified. Sub slot before first conversion (a1 , b1) Sub slot after first conversion (a1', b1') (0 , 0) (1 , 0) (0 , 1) (1 , 1) (1 , 1) (0 , 1) (1 , 0) (0 , 0) Sub slot before second conversion (a1 , b1 , c1) Sub slot after second conversion (a1' , b1' , c1') (0 , 0 , 0) (0 , 1 , 1) (0 , 0 , 1) (0 , 1 , 0) (0 , 1 , 1) (1 , 1 , 0) (0 , 1 , 0) (1 , 1 , 1) (1 , 1 , 0) (1 , 0 , 1) (1 , 1 , 1) (1 , 0 , 0) (1 , 0 , 1) (0 , 0 , 0) (1 , 0 , 0) (0 , 0 , 1) First waveform memory First addressing pattern (a1) Waveform data to be stored 0 33A 1 33D Second waveform memory Second addressing pattern (b1) Waveform data to be stored 0 33C 1 33B

Claims: A waveform shaping equipment comprising: a pulse waveform generating means (J111, J171, J191) for inputting a data string, said data having a symbol duration (T), and generating and outputting a first waveform which is the first half of a band-limited pulse waveform corresponding to each symbol of the data string and a second waveform which is the latter half of the band-limited pulse waveform, and a waveform processing means (J112, J142) which has adding means (J113, J143) which inputs the first and the second waveforms and adds the first waveform and the second waveform to generate a third waveform as a shaped waveform so that in each symbol interval, the second waveform represents the latter half of the pulse corresponding to the preceding data and the first waveform the first half of the pulse corresponding to the succeeding data. The waveform shaping equipment according to claim 1, wherein the waveform processing means (J112, J142) outputs zero-level waveforms whose level is zero before the start of the data strings to be transmitted, outputs the first waveform for one symbol time from the start of the data string to be transmitted, outputs the second waveform for one symbol time from the end of the data string to be transmitted, and thereafter outputs the zero-level waveforms until the next data string to be transmitted starts. The waveform shaping equipment according to claim 1, wherein the waveform processing means (J112) has a waveform selecting means (J114) for inputting a zero-level, the first, second, and third waveforms and being adapted to select any of the input waveforms in order to output said zero-level waveform before the start of the data strings to be transmitted, the first waveform for one symbol time from the start of the data string to be transmitted, the second waveform for one symbol time from the end of the data string to be transmitted, and thereafter the zero-level waveform until the next data string to be transmitted starts. The waveform shaping equipment according to claim 2, wherein the waveform adding means (J143) has a first input terminal (J1412) for inputting the first waveforms and a second input terminal (J1413) for inputting the second waveforms, the first and the second input terminals (J1412, J1413) are designed to be cut off, respectively, and when the first waveforms are outputted as shaped waveforms, the second input terminal (J1413) is cut off, and when the second waveforms are outputted as shaped waveforms, the first input terminal (J1412) is cut off, and when the zero-level waveforms are outputted, both first and second input terminals (J1412, J1413) are cut off. The waveform shaping equipment according to any of claims 1 to 4, wherein the pulse waveform generating means (J111, J171, J191) comprises memory table (J115, J116, J1716, J1916) for storing the first and the second waveform data, an addressing signal generating means (J117, J178, J1719, J198, J1923, J1924, J1925) for generating addressing signals for reading out data related to waveforms from a specified position of the memory table (J115, J116, J1716, J1916), and the memory table (J115, J116, J1716, J1916) is designed to be retrieved by the addressing signals to read and output the first and second waveform data. The waveform shaping equipment according to claim 5, wherein the addressing signal generating means (J117, J178, J1719, J198, J1923, J1924, J1925) comprises a shift register (J118, J178, J198) for accumulating data for the latest 2 symbols of data strings and outputting them in parallel and a cyclic counter (J119, J1719, J1924, J1925) which has a period equal to the symbol time, and the addressing signal for reading out the first waveform comprises the first-stage output of the shift register (J118, J178, J198) and the output of the counter (J119, J1719, J1924, J1925), and the addressing signal for reading out the second waveform comprises the second-stage output of the shift register (J118, J178, J198) and the output of the counter (J119, J1719, J1924, J1925). The waveform shaping equipment according to claim 5, wherein the waveforms obtained by inverting the first waveform with respect to time is used for the second waveform and the pulse waveform generating means (J171, J191) generates the first waveform and the second waveform from the same data of the memory table (J1716, J1916). The waveform shaping equipment according to claim 7, wherein, when the second waveform data is read out, the addressing signal generating means (J198, J1923, J1924, J1925) generates addressing signals in the sequence reversal to that of the addressing signals, with respect to time, when the first waveform data is read out in each symbol time. The waveform shaping equipment according to claim 5 or 8, wherein the addressing signal generating means (J117, J178, J1719, J198, J1923, J1924, J1925) is designed to generate addressing signals for reading out the first waveform data and addressing signals for reading out the second waveform data alternately, and the pulse waveform generating means (J111, J171, J191) is designed to read out the first waveform data and the second waveform data alternately from the memory table (J115, J116, J1716, J1916).

Inventors: KAI KOJI, KOGA SHOUICHI, TAKAI HITOSHI, URABE YOSHIO, YAMASAKI HIDETOSHI, KAI, KOJI, KOGA, SHOUICHI, TAKAI, HITOSHI, URABE, YOSHIO, YAMASAKI, HIDETOSHI
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1994
Main classification: H04L25
IPC codes: H04L27, H04L25, H03G3